The present invention relates to optimum control techniques for fuel flow quantity and an ignition timing for an internal combustion engine, and more particularly, to a diagnosis method and a diagnosis apparatus for a control unit of an internal combustion engine which are suitable for an optimum control system, and a fuel control system utilizing the same.
Under the same operating conditions which become the basic conditions, such as a quantity of fuel, number of engine revolutions, load, fuel properties, etc., an internal combustion engine changes its operating torque when the fuel quantity or the ignition timing is fine adjusted, and there exist optimum values for the fuel quantity and the ignition timing at which the engine generates a maximum torque. Accordingly, it is clear that the fuel consumption rate of the internal combustion engine will be improved if the fuel quantity and the ignition timing are continuously varied so as to yield the maximum torque under different operating conditions.
It has hithereto been proposed that an actual internal combustion engine is controlled in accordance with a map data which has been prepared in advance to indicate the fuel supply quantity and the ignition timing at which a maximum output is generated in response to the number of engine revolutions and load on the internal combustion engine. However, the optimum fuel quantity and ignition timing fluctuate with behaviour of individual engines and due to ageing caused by carbon deposites, sensor drift, actuator drift, and in the use of fuels with different octane numbers. It has, therefore, been extremely difficult to control the engine in proper response to such fluctuating conditions.
In the mean time, an article published in the SAE PAPER (SAE) 870083 (February 1982) pp. 43-50 discloses a method for predicting an ignition timing which gives a maximum torque output from a detected rate of change of rotation of an internal combustion engine when the engine speed is changed by increasing or decreasing the ignition timing while the internal combustion engine is running. This is a method for moving the ignition timing advance angle in proportion to the gradient of the output torque of the internal combustion engine.
Thus, denoting the output torque of an internal combustion engine by T, denoting the number of engine revolutions by N, and denoting the ignition advance angle by .theta., then the following formula applies: ##EQU1## An optimum control is, therefore, achieved by applying the so-called hill-climbing method; that is to say instead of determining the change gradient of output torque to ignition advance angle (.DELTA.T/.DELTA..theta.), a change gradient of the number of revolutions of the internal combustion engine to ignition advance angle (.DELTA.N/.DELTA..theta.) is determined, and the amount of the ignition advance angle is moved in proportion to the gradient of the characteristic .DELTA.N/.DELTA..theta..
The above method, however, has a problem in its signal-to-noise ratio. By nature, an internal combustion engine has subtle revolutional variations attributable to various factors. These variations in the revolutions become noise components due to changes of the engine revolutions in response to increase or decrease of an ignition timing. In order to obtain sufficient detection sensitivity of a changing signal which can be discriminated from the noise components, it is necessary to take a large width for the increase and decrease of the ignition timing so as to take a sufficiently large quantity of variations of the revolutions of the internal combustion engine. These large variations of revolutions give a large schock to car drivers who are expecting normal smooth driving conditions, and are never desirable because of aggravated driving comfort and drivability.
It is an object of the present invention to provide a new method for obtaining an optimum control value of a control system for an internal combustion engine by providing a minimum change in its operating state within a range in which a normal operation of the internal combustion engine is not interrupted, and also to provide a diagnosis method for an internal combustion engine utilizing the above method, an optimum control method for a fuel flow quantity and an ignition timing, and a control apparatus which can utilize these methods.